This application claims the priority of German patent application No. 198 13 673.0, filed Mar. 27, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a particular method and a particular device for heating and cooling a compartment.
EP 0 424 474 B1 describes a method and a device for operating a transcritical vapor compression circuit. A compressor, a radiator, an expansion unit, and an evaporator are connected in series with one another by lines carrying coolant, and form an integral circuit for the coolant. In this circuit, the pressure on the high-pressure side is above the critical pressure of the coolant.
However, the method known from this publication has the disadvantage that the cooling power is controlled by changing the specific enthalpy of the coolant by varying the pressure and/or the temperature. Efficient power regulation with a supercritical process pressure is not feasible with the method and the device described in EP 0 424 474 B1, since environmental influences, such as outside temperature, humidity, solar radiation and so on, severely interfere with the control of the cooling power by differences in enthalpy of different degrees in the evaporator. A considerable regulation expense is required for regulating power in this way.
DE 44 32 272 C2 describes a method for operating a cold-generating system for air-conditioning vehicles. The cold-generating system comprises, as circuit components, a compressor, a heat exchanger, an expansion unit, and an evaporator, which are connected in series and form an integral closed circuit for the coolant. To produce cooling power, the circuit is operated on the high-pressure side at a supercritical pressure and, simultaneously, on the low-pressure side at a subcritical processing pressure. Heat energy is supplied to the coolant on the high-pressure side. The mass flow of the coolant in the circuit is varied by regulating the throughput of the coolant in the compressor.
The disadvantage of this method is that the compartment of a vehicle can be air-conditioned only under certain conditions since the compartment air flow supplied to the compartment can essentially only have energy withdrawn from it. Only cooling of the compartment is possible with this cold-generating system.
Hence, one object of the present invention is to expand a coolant circuit that essentially operates transcritically for air conditioning vehicles in such a fashion that the heating power transferred to the compartment air is provided efficiently, comfortably, and at a certain temperature level. Additionally, it is an object of the invention to provide a modern vehicle concept for air conditioning an interior of a motor vehicle which provides required cooling or heating power nearly independently of the operating state of the internal combustion engine and of influences in the environment such as the outside temperature, humidity, solar radiation, etc.
This object is achieved according to the invention, during a cooling operation, by conducting a medium in the circuit through a compressor, an ambient heat exchanger, a throttle device, and an interior heat exchanger, which are connected in series and form an integral closed circuit. A supercritical pressure is produced on a high-pressure side of the circuit and, at the same time, a subcritical pressure is produced on the low-pressure side of the circuit. On the low-pressure side of the circuit, heat is supplied to the medium in the circuit through the interior heat exchanger. The mass flow of the medium in the circuit is varied by regulating the throughput of the medium in the circuit in the compressor.
During a heating operation, the medium in the circuit is conducted sequentially through the compressor, the interior heat exchanger, the throttle device, the ambient heat exchanger, and/or an exhaust heat exchanger. Consequently, the high-pressure side of the circuit during the cooling operation becomes the low-pressure side and the low-pressure side of the circuit during the cooling operation becomes the high-pressure side. The medium in the circuit is guided in the interior heat exchanger at a supercritical pressure, and heat from the medium in the circuit is transferred to the compartment air being supplied to the compartment. The mass flow of the medium in the circuit is regulated by regulating the throughput of the medium in the circuit in the compressor. Additionally, the pressure in the interior heat exchanger is regulated to a value below an admissible pressure.
A particular device according to the invention operates such that, during the heating operation, the compressor, the interior heat exchanger, the throttle device, the ambient heat exchanger, and the exhaust heat exchanger are connected in series and a medium in the circuit can be expanded in the throttle device to a temperature below an intake temperature of the medium in the circuit in the compressor. The medium can be exposed to ambient air in the ambient heat exchanger, heated in the exhaust heat exchanger by exhaust from the engine, and compressed in the compressor. During the cooling operation, the compressor, the ambient heat exchanger, the throttle device, and the interior heat exchanger are arranged in series, and the medium in the circuit may be exposed to ambient air in the ambient heat exchanger and expanded in the throttle device to a temperature below a compartment air temperature. The compartment air can be exposed to the medium in the circuit in the interior heat exchanger.
With the method according to the invention, the mass flow of medium in the circuit is varied as required in an advantageous fashion as a function of the required heating power and the quantity of heat supplied from the environment and/or the exhaust heat from the engine. As a result, air conditioning permanently installed according to the prior art for cooling can be used in a simple fashion for heating the interior of the motor vehicle.
It is also advantageous that only that compressor power that is absolutely necessary for comfortable heating is drawn and the temperature of a medium in the circuit is maintained in the interior heat exchanger at a temperature level such that a suitable temperature of the compartment air is ensured for safe operation of the motor vehicle in traffic.
In an advantageous fashion, when the device according to the invention is used for heating a compartment of a motor vehicle, the medium in the circuit is successively expanded in the throttle device to a subcritical process pressure, heated in the ambient heat exchanger and/or the exhaust heat exchanger, compressed in the compressor to a supercritical process pressure, and cooled in the interior heat exchanger with cold compartment air, so that the compartment can be heated with the heated compartment air.
Another advantage of operating the circuit under subcritical process conditions is that no phase change of a circulating medium takes place in the interior heat exchanger. Instead, the circulating medium is permanently conducted in the subcritical range through the interior heat exchanger and, therefore, a much higher quantity of heat can be transferred from the circulating medium to the compartment air. A much higher efficiency is achieved in the circulating process than in conventional circulating processes that operate in the subcritical range.
By regulating or controlling the throughput of the compressor in combination with the heat uptake by the ambient heat exchanger, it is possible to react flexibly and rapidly to desired temperature changes in the compartment air in the compartment or to compensate flexibly and rapidly for influences such as intense solar radiation.
It is especially advantageous in a supercritical process that a much higher quantity of heat can be transferred from the circulating medium to the compartment air supplied to the compartment with known heat exchangers, since the circulating medium is conducted at a much higher temperature through the interior heat exchanger. This ensures that components already present and known from the prior art can be used without any design changes.
The arrangement of the components according to the invention makes possible a thermodynamic circulating process in which the heating power can be provided to a sufficient degree in a simple manner under nearly all operating states of the internal combustion engine.
In addition, the supplementary vehicle heating that is provided routinely can be eliminated, thus resulting in weight production and hence a reduction of fuel consumption by the motor vehicle in an advantageous manner.